Acute viral myocarditis is an important human disease. While enteroviruses cause immune-mediated damage, the mechanisms by which other viruses induce myocarditis remain largely unexplored. Reovirus- induced murine myocarditis is not determined by immune cell function, and presents an ideal model for studying nonimmune mediated myocarditis. Our data suggest that differential induction of and sensitivity to interferon-beta (IFN-beta) in cardiac myocytes are determinants of reovirus-induced myocarditis, and that these activities are determined by reovirus core proteins involved in RNA synthesis. IFN provides a critical first line of defense against viral infection. Viral RNA synthesis stimulates cell factors which regulate IFN-beta transcription. Secreted IFN binds receptors and induces IFN-responsive genes which mediate IFN's antiviral effects, but several of these require double stranded-[ds]RNA activation. Both induction of and sensitivity to IFN- beta are highly dependent on virus strain and cell type, and yet, there have been no studies on the cardiac IFN response to viruses. Our first hypothesis is that differential induction of IFN-beta by reovirus infection is determined by differential induction or activation of PKR, IRF-1, and/or IRF-2. In Specific Aim 1, we will determine whether PKR (dsRNA activated protein kinase), IRF-1 (IFN regulatory factor-1) and/or IRF-2, each of which regulate IFN-beta induction in other virus/cell systems, regulate reovirus induction of IFN-beta in primary cardiac myocyte cultures, and we will use knockout mice to investigate their roles in vivo. In Specific Aim 2, we will use two additional cell types to identify cell-specific responses. Our second hypothesis is that differential sensitivity to IFN-alpha/beta is due to differential activation of and/or sensitivity to PKR, 2',5'-oligoadenylate synthetase, and/or RNase L. In Specific Aim 3, we will determine whether these three factors, each of which requires dsRNA activation for antiviral effects in other virus/cell systems, mediate reovirus sensitivity to IFN-alpha/beta in primary cardiac myocyte cultures, and we will use knockout mice to investigate their roles in vivo. In Specific Aim 4, we will use two additional cell types, as above. Reoviruses offer a unique tool to investigate the IFN response invoked by closely related viruses in the heart. Our work will be the first to identity cell factors that are determinants of this cardiac IFN response and myocarditis.